1. Field of the Invention
This invention relates to clutch actuating systems, and, more particularly, to actuating systems for automotive clutches in which a largely conventional diaphragm spring is combined with a positive spring device to reduce control force needed for clutch actuation to a predictable, relatively small, and essentially constant force value.
2. Description of the Related Art
In pending U.S. applications Ser. No. 08/746,887, Ser. No. 08/791,524, and Ser. No. 08/888,832, the disclosures of which are incorporated by reference, control force actuating systems are disclosed in which a negative Belleville spring is arranged in series with a positive spring unit such that as force application energy is released from the negative Belleville spring, that energy is transferred between load and reaction members by the positive spring. The force/deflection characteristics of the negative Belleville spring and positive spring unit are related so that the difference in energy stored in the respective springs throughout a range of force application, remains substantially the same. As a result, the control force required to operate the actuating system is related to the stored energy difference and can be kept very small. The relatively small control force required for such actuating systems represents a significant step toward automated actuation of an automotive clutch, for example, by using state-of-the-art electromechanical transducers exemplified by an electromagnetic solenoid.
The diaphragm spring conventionally used in modern automotive clutches is typically configured with a continuous outer annulus defining a Belleville spring and joining with inwardly directed radial fingers to which an axial control force is applied. A diaphragm fulcrum is provided at the juncture between the inner edge of the outer annulus and the outer edges of the fingers. Also, a circular array of holes in the region of the fulcrum are used to support the diaphragm from the backplate or cover plate of the clutch on axial fulcrum rivets or pins. Fulcrum rings prevent movement of the diaphragm fulcrum axially on the pins while allowing the required amount of movement at the outer periphery of the annulus and at the inner ends of the control fingers. Such diaphragm springs enable high loads to be generated through small displacements and contribute to compactness and high torque transmitting capabilities.